1. Field of Application
This invention is about a high lumen output Cold Cathode Fluorescent lamp (CCFL). It can be used for lighting applications that requires high lumen output, such as for street, tunnel, signage, bridge, building, shopping mall, square, etc. It can be used to replace the High Pressure Sodium lamp, High Pressure Mercury lamp, Electrodless lamp, Metal Halide lamp and High Power Hot Cathode Fluorescent Lamp. It can also be used as lamps with adjustable color temperature, dimming, multiple colors and adjustable multiple colors.
2. Technical Background
The current lighting technologies for street lighting with high lumen output mainly include Low Pressure Sodium lamp, High Pressure Sodium lamp, High Pressure Mercury lamp, Electrodless lamp, and Metal Halide lamp.
The Low Pressure Sodium lamp has Photopic vision efficiency of 180 lm/W, but its CRI (correlated color index) is very low, and is seldom used now.
High Pressure Sodium lamp has Photopic efficiency of 90˜120 lm/W and lifetime up to 25,000 hours. It has been the main source for street and tunnel lighting. China's 80% street lamps use High Pressure Sodium lamp. But this lamp's CRI is also very low, about 20˜25. Its color temperature is 2000˜2400 Kelvin, which is a yellowish light. Its' Mesopic vision/Photopic vision=0.6 and its Mesopic vision efficiency is about 54˜56 lm/W. Its ability to distinguish object is very poor and its ability to identify object is also very low, not good for safety reason. The high CRI white color High Pressure Sodium lamp only has efficiency of 37˜48 lm/W.
The High Pressure Mercury lamp has efficiency of 50 lm/W; its CRI is about 45 and its lifetime is short. It is seldom used now.
The Electrodless lamp has long lifetime, with CRI>80, and a lamp system efficiency (including driver consumption)>60 lm/W. But its high cost and high electromagnetic interference severely restricts its applications.
The Metal Halide lamp's CRI is between 65˜92, its lamp efficiency between 72˜95 lm/W, its color temperature between 3000˜5600 Kelvin, and its lifetime between 6,000˜20,000 hours. But its lumen output decays rapidly; the uniformity of lamp color temperature is also poor, and the lamp system efficiency low. When input power variation is more than +/−10%, its color will change. The position of the lamp's cold point and its installation can easily affect the lamp's color temperature and lifetime. This type of lamp needs 5˜15 minutes to get started. It will need another 10˜15 minutes for restarting once it is turned off. The surface temperature of the lamp is very high. The sodium within the quartz lamp will migrate and cause the lamp's light color to change. The reaction between quartz—metal, and quartz out gassing will also shorten the lamp's lifetime. Its cost is also high. Its application for street and tunnel lamp is still very limited.
The current Cold Cathode Fluorescent lamp (CCFL) technology provides advantages such as lifetime of >20,000 hours (with LCD CCFL backlight providers claiming >50,000 hours), On/Off switching of over 108 times, lamp system efficiency of >55 lm/W, and CRI>80. It has been used in broad applications in the LCD backlight system. It has also been used for making 2˜8 W low power spiral shape energy saving lamps. The Cold Cathode Fluorescent lamp operates in the normal glow region of the Gas Discharge lamp I-V curve. Its cathode drop is about 145V, and its anode drop about 10V. According to the traditional theory, the CCFL works in the normal glow gas discharge field and its operating current is of the order of about 10−4˜10−2 A. Please see FIG. 2-24 on page 92 of “” 2004, , , ISBN 7-111-13283-1 (“Lighting Technology Handbook,” by Zu Xiao Qing, China Mechanical Industry Publishing Company, 2004, p. 92). This figure is reproduced as FIG. 21 of the present application. According to the traditional theory, the CCFL normal operating current is 5 mA and the upper limit is 8-10 mA. If the current is increased to above this upper limit, then the gas discharge will move into the abnormal glow region and its cathode drop will increase rapidly and cause great loss in efficiency. Also the cathode temperature will rapidly increase, causing the rate of metal sputtering in the cathode to increase rapidly and shortens the lamp lifetime. The CCFL lifetime is inversely proportional to the square of its operating current according to the following formula:CCFL lifetime=K/I2.
Where K is a constant, I is the operating current.
The above limitation is the main reason why up to now the CCFL can only be used for making lower power lamp. For example, the maximum voltage is 1500V, and the current is 10 mA. The maximum lamp power is only 1500×0.01=15 W. If one attempts to increase the current supplied to the CCFL, its life time decreases with the square of the current, which is undesirable. That is why up to now CCFL has never been considered as a good candidate for general lighting as its lumen output is limited because everyone believes that the best CCFL operating range in the “Normal Glow Discharge” region for operating current is 5 mA.
According to the traditional theory of CCFL, the CCFL's best efficiency occurs when the internal diameter (ID) of its lamp tubing is between 1.2˜2 mm, and its outside diameter (OD) is less than 2˜4.1 mm. If larger diameter lamp tubing is used for the CCFL, its lumen output efficiency will greatly decrease due to the effect of the increase in self absorption among its radiation photons and voltage drop in the lamp tubing of the lamp. According to the traditional theory of CCFL, it is a highly difficult technical problem to produce high efficiency CCFL with high lumen output of several thousand lumen or higher. That is why the currently available Cold Cathode Fluorescent lamp cannot be used to replace the High Pressure Sodium lamp, High Pressure Mercury lamp, Electrodless lamp, Metal Halide lamp and high power Hot Cathode Fluorescent lamp in the applications for street lighting, tunnel lighting, signage lighting, and in places like bridges, buildings, malls, public squares that require large lumen output for illumination.
The Neon Light is very similar to CCFL, as it is also a light source that functions in the normal glow region of the Gas Discharge I-V curve. The Neon Light uses large diameter glass lamp tubing, large operating current, such as 25˜60 mA, several thousand to twenty thousand volt as its operating voltage, low current density on its lamp and lamp operates in close to room temperature. Its white color light efficiency is only 15˜30 lm/W and its lifetime are roughly 3,000 hours. It is mainly used in advertising display. It is not possible to use the current neon technology to make high efficiency and long lifetime lamp for street and tunnel lighting.